Rythme game and timer problem

Hello guys.

I make a rythme game in UE4.

I have many problem with the time in UE4.

I created an area on the ground with a collision box , and this area counts the points(with a timer) of which the character enters in.
I move the character with a timeline.
As soon as the character enters in the zone the counter starts ,as soon as it comes out the meter stops.

The timer counts how long the player is in the counter zone in msecond
The problem is that I’m never the same value in the timer.
1.98s etc etc…
I move my character with a sequencer and my counter point is a set timer by event with looping every 0.1s.
What is the problem with the timer?
Why i have not every time the same result?
I do not use tick because I saw that it is dependent off fps.


Sorry for my bad english , but i have a picture lol.